This application claims priority under 35 U.S.C. Sec. 119 to No. 2000-42086 filed in Japan on Feb. 18, 2000, the entire content of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to a brake control system for a vehicle, which is adapted to perform a traction control, anti-skid control, steering control by braking and other various controls, and especially relates to the brake control system having automatically pressurizing means for advancing a master piston irrespective of operation of a brake pedal to generate hydraulic braking pressure from a master cylinder.
2. Description of the Related Arts
In Japanese patent No. 2790288, which corresponds to the U.S. Pat. No. 4,966,248, there is disclosed a traction control system, wherein fluid pressure produced by a master cylinder is provided by actual pressure on a brake pedal together with supplemental pressure provided by a vacuum servo unit incorporating an electromagnetic valve. When the electromagnetic valve is de-energized, it allows the servo unit to only operate to provide-supplemental pressure when pressure is applied to the brake pedal, and when energized, it connects the servo unit to atmosphere so that the servo unit can by itself apply fluid pressure to a wheel brake via the modulation unit. The electromagnetic valve is energized when a wheel commences to spin faster than the other wheels.
It is described in the patent that the system includes a normally open solenoid valve 1,5 and a normally closed solenoid valve 16, and includes a-solenoid valve 35 which is connected to the servo unit 13 and energized for controlling traction. The braking force applied to the wheel can be controlled in the same manner as with an antilock system with the fluid being returned by al pump to the master cylinder.
According to the traction control system as disclosed in the above-described patent, the brake fluid in a reservoir is returned by the pump to the master cylinder. In that system, if the communication between the master cylinder and all of the wheel brakes (wheel brake cylinders) are blocked during the traction control, the hydraulic pressure in the master cylinder is so high that the brake pedal can not be operated. In the case where it is so constituted that the operation of the brake pedal is detected by a stroke of the brake pedal, therefore, the operation can not be detected in the above case, so that the traction control can not be terminated, even if the brake pedal was operated during that control. Of course, brake feeling to a driver will not be appropriate, in that case.
Accordingly, it is an object of the present invention to provide a vehicle brake control system having an automatically pressurizing device for advancing a master piston irrespective of operation of a brake pedal to generate hydraulic braking pressure from a master cylinder, wherein a brake pedal stroke can be ensured, even if the communication between the master cylinder and all of wheel brake cylinders is blocked during a hydraulic pressure control.
In accomplishing the above and other objects, the vehicle brake control system includes wheel brake cylinders operatively mounted on wheels of a vehicle, respectively, a master cylinder for advancing a master piston at least in response to operation of a brake pedal to supply brake fluid to the wheel brake cylinders, a reservoir communicated with the wheel brake cylinders for storing the brake fluid drained therefrom, normally open solenoid valves disposed between the master cylinder and the wheel brake cylinders, respectively, normally closed solenoid valves disposed between the wheel brake cylinders and the reservoir, respectively, and a hydraulic pump for introducing the brake fluid stored in the reservoir and supplying the brake fluid to a passage for connecting the master cylinder with the normally open solenoid valves. The system further includes an automatically pressurizing device which is provided for advancing the master piston irrespective of operation of the pump and the brake pedal to generate hydraulic braking pressure from the master cylinder, and a controller which is provided for actuating the normally open solenoid valves, the normally closed solenoid valves, the pump and the automatically pressurizing device, to control the hydraulic braking pressure in the wheel brake cylinders. The controller is provided for controlling a distance of the master piston, which is advanced by the automatically pressurizing device when all of the normally open solenoid valves are closed during the hydraulic pressure control of the wheel brake cylinders, to be greater than the distance of the master piston, which is advanced by the automatically pressurizing device when at least one of the normally open solenoid valves is open during the hydraulic pressure control of the wheel brake cylinders.
According to the system as described above, the stroke of the brake pedal can be ensured, even if the communication between the master cylinder and all of the wheel brake cylinders is blocked during a pressure control. Therefore, a traction control can be terminated in response to a variation of the stroke of the brake pedal, for example.
In the system as described above, the controller may be adapted to execute a specific terminating control, by which the automatically pressurizing device is actuated for a predetermined time period after the hydraulic pressure control of the wheel brake cylinders is terminated, with all of the normally open solenoid valves closed, to provide the maximum distance of the master piston advanced by the automatically pressurizing device. According to this system, if the automatic pressurization performed by the automatically pressurizing device starts within the predetermined time period after the previous automatic pressurization was terminated, the automatically pressurizing device is being actuated during that period. Therefore, frequent stopping and starting the device can be avoided. During the specific terminating control, all of the normally open solenoid valves are closed, so that the master cylinder pressure generated by the automatically pressurizing device can be avoided from being supplied to the wheel brake cylinders. Furthermore, the maximum distance of the master piston is advanced by the automatically pressurizing device during the specific terminating control, so that the stroke of the brake pedal can be ensured, even when all of the normally open solenoid valves are closed during the specific terminating control.
In the system as described above, the controller may be adapted to execute a delay control, by which the pump is actuated for a predetermined time period after the hydraulic pressure control of the wheel brake cylinders is terminated, and adapted to prohibit the delay control, in the case where the specific terminating control is executed, and where the brake fluid in the reservoir is less than a predetermined amount when the brake pedal is not operated. According to this system, it can be avoided that the brake fluid in the reservoir is returned to the master cylinder by means of the pump during the specific terminating control. Therefore, the stroke of the brake pedal can be ensured certainly.
Preferably, the controller may be adapted to execute the specific terminating control only when the brake pedal is not operated. Accordingly, the master cylinder pressure can be certainly supplied to the wheel brake cylinders in response to operation of the brake pedal.